With the advent of digital lighting control networks, lighting control systems for professional applications, e.g. for office buildings, have become very sophisticated. The different luminaires disposed in the rooms of the building can be controlled on the basis of sensor data so that each individual luminaire can be controlled to produce the required lighting situation. The control is performed by a central control unit responsible for all luminaires of the lighting system. The sensor data are received by the central control unit that sends control commands to the respective luminaires. For this purpose the central control unit comprises processing means to perform an algorithm to compute the control commands. These processing means may also include a memory for storing necessary data, configuration values, addresses and physical locations of the sensors and of the luminaires to which the control commands are sent, and so on.
The luminaires, the sensors and the central control unit are connected by a network that establishes a communication between these elements of the lighting systems. This architecture is shown schematically in FIG. 1. Each luminaire 10, 12, 14, 16, 18 is connected to the network 20, as well as the central control unit 22, to establish a communication between the luminaire 10, 12, 14, 16, 18 and the central control unit 22. Moreover, sensors 24, 26 are arranged to send sensor data via the network 20 to the central control unit. On the basis of these sensor data, a central control unit 22 computes control commands for each luminaire 10, 12, 14, 16, 18. It is noted that each sensor 24, 26 is associated to at least one luminaire 10, 12, 14, 16, 18, i.e. the respective luminaires 10, 12, 14, 16, 18 receive control commands by the central control unit 22 that are computed on the basis of sensor data of their associated sensors 24, 26. For example, one sensor 24 is arranged in one room where his respective associated luminaires 10, 12 are disposed. On the basis of the sensor data of this sensor 24, the luminaires 10, 12 are controlled. Another sensor 26 in another room is arranged for providing sensor data to control the respective luminaires 16, 18 in this room, etc.
The network 20 can be represented, for example, by an IP (Internet Protocol) Network so that each element, i.e. the central control unit 22, the luminaires 10, 12, 14, 16, 18 and the sensors 24, 26 can communicate to any other device, and each unit is provided with an individual IP address. However, any other suitable network types or architecture can be used in this context.
The use of one single central control unit 22 to control multiple luminaires 10, 12, 14, 16, 18 provides a number of advantages in view of costs and configuration flexibility. However, there is a serious disadvantage in view of robustness of the communication architecture. In case the central control unit fails to operate, all luminaires usually controlled by the central control unit during standard operation are without control. On the other hand, the provision of a “backup” central control unit would increase the costs and the complexity of the lighting control system in an unacceptable way. Moreover, such a backup control unit would be of no use in the case of a failure or breakdown of the network communication between the central control unit and the luminaires or sensors.